Automatically Change Font Size On Selection

I use this ok code to increase the font in the selected cell:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim TargetRange As Range
Dim isect
Set TargetRange = Range("C:D")
Set isect = Intersect(Target, TargetRange)
If Not isect Is Nothing Then
Columns("C:D").Font.Size = 11
Target.Font.Size = 15
Exit Sub
End If
Columns("C:D").Font.Size = 11
End Sub

The problem is when i press ctrl+c to copy a cell content, so once i move the curser to the distenation cell then the copying mode in selected cell disappeared.
It is because when the event is trigered then the copying mode stops. The question is : how to let the copying mode works even when the event is trigered ?